Yes, and you can see that very consistently in the modelled position of the Scandi-H: it systematically tends to be placed much higher, even elongated. Wether that is good or not remains to be seen but it is a big difference with the december situation! Back then it was always the question: will it be MLB or HLB.

It seems to me that in most models a slight HP zone above Greenland steers the energie more southward and thus creates a delicate balance between the heavy atlantic and HP above the continent. I can imagine that a small difference in the upstream modelling will create a large difference in the downstream battle...

Models are what they are: models! They take into account what their creators know about the atmospherical processes and that is a lot. But there is also a lot they don't know or are unable to bring into the models. There is a lot of uncertainty, exponentially increasing after D1. When you can't stand this uncertainty don't look at models!

An excellent wrap-up of developments i think. But it still strikes me as strange that ECM and GFS model so differently in a situation where there are, as you say, few major forcings taking place. In a relative quiet environment every model should be down to basic airo-, thermo- and other dynamic models..?

Hmm, awfully quiet over here. I might be completely wrong but is there a reversal in the making? Temps at 30 hPa are rocketing up like early Januari. At 10hPa less pronounced though. I can imagine that these observations are illustrating the shift of the strat-vortex away from the pole?

Yes, Is it correct to state that It requires more energy to disturb a strong vortex but when it happens the effects will be more spectacular? And: a weakened vortex is easier to disturb but the effects are less? There is a lot in between these.... On the other hand: a strong trop-jet (caused by a strong start PV) creates more energy and chances for MT's and warming are bigger. Its all a matter of balance but Ideally it would be a weakened strat PV and relative strong trop-jet?

That's the point I tried making yesterday evening. The Skandi-high is troposferically holding on due to stratosferical weakening and displacement. Both Gfs and ECM support this up to T240. Chio: in line with your image of two dancers: the troposferic one leads the dance here because the stratosferic dancer allows it or is not able to the take the lead. I expect the first cold spells late nov/early dec. It won't be "big-time" but the first dance sets the tone...

I think the developments arround T240 are quite interesting: both GFS and ECMWF predict ridging at 500HPA in the direction of Iceland/Greenland: This introduces a cold spell from the North. http://www.wetterzentrale.de/pics/Recmnh2401.gif https://max.nwstatic.co.uk/gfsimages/gfs.20141115/18/240/npsh500.png the, at that time reinforcing, stratosferic vortex also positions in that place: https://max.nwstatic.co.uk/gfsimages/gfs.20141115/18/240/npst30.png I don't know but it looks to me that at this stage the (shattered) troposferical vortex determines the development of the stratosferic vortex and not the other way. .

yeah, that's truth but what I mean is: it will land somewhere either displaced or splitted. Can we say something about the effects that specific "landing-places" have on the tropospheric vortex and thus on the effects on the winter-weather? I know I am placing a big question and I know that understanding the behaviour of the stratospheric vortex is still in early investigation but in-the-end its is all about the effects this has on the troposherical conditions!

Thanks Chio for your excellent baseline posting! I am following this thread for a couple of years now and I am learning a lot! What still puzzles me very much is the positioning of the stratospheric vortex in wintertime. Clearly a strong vortex will be highly central to the noth-pole but when weakened, displaced or even split, where will it "land"!? And what effect will that position have on the troposferic position. It seems to me this is a question we should be investigating to understand the stratosphere/troposphere coupling and effects on tropospheric blocking?